The present invention relates to a reflection liquid crystal projector designed so that a colored image, which are synthesized from the images of a first, a second and a third colors (e.g., R, B and G lights) formed on a first, a second and a third panels (e.g., reflection panels for R, B and G) respectively, can be projected on a screen through a projection lens.
Conventionally, it has been a common practice that a reflection liquid crystal projector has a composition as is shown in FIG. 1. That is, the white light outputted from a light source 10 is converted into an S-polarized light by a polarized light conversion element 12; of the S-polarized light, the R light (Red light) is separated from the B light (Blue light) and G light (Green light) by a cross dichroic mirror 14; the B and G lights are led to the dichroic mirror 18 by means of a cross dichroic mirror 14; the B and G lights are led to the dichroic mirror 18 by means of a total reflection mirror 16 to be separated into the B light and G light.
The separated R light is led to a first polarization beam splitter 22 (hereinafter referred to the first PBS) by a total reflection mirror 20; the R light is reflected by the polarizing film of the first PBS to fall on a reflection liquid crystal panel 24 (hereinafter referred to as the LCD for R), and the reflected light (converted into a P-polarized light from an S-polarized light) is outputted through the splitter 22.
The separated B light is reflected by the polarizing film of a second polarization beam splitter 26 (hereinafter referred to as the second PBS) to fall on a reflection liquid crystal panel 28 (hereinafter referred to as the LCD for B), the panel being provided for the display of B image, and the reflected light (converted to P-polarized light from the S-polarized light) is outputted through the beam splitter 26.
The separated G light is reflected by the polarizing film of a third polarization beam splitter 30 (hereinafter referred to the third PBS) to fall on a reflection liquid crystal panel 32 (hereinafter referred to as the LCD for G), the panel being provided for the display of a G image, and the reflected light (converted to P-polarized light from S-polarized light) is outputted passing through the beam splitter 30.
A cross prism 34 not only reflects the R and B lights, outputted from the first and the second PBS""s 22 and 26, but also passes the G light outputted from the third PBS 30 to synthesize the R, B and G lights to display a colored image by projecting the synthesized light on a screen (not shown) through a projection lens 36.
However, such a conventional method shown in FIG. 1 has problems as are given below.
(1) Using an expensive cross prism 34 as a color synthesizing element results in the high price of a projector. More specifically, using the cross prism, which is to be assembled with four parts, results in low yield, high price and increase in weight of the projector.
(2) Needing 3 PBS""s, i.e., the first PBS 22, the second PBS 26 and the third PBS 30, contributes not only to a high cost but also an increase in weight.
The present invention is made in consideration of the above-mentioned problems and is intended to provide a low-price and lightweight reflection liquid crystal projector by eliminating the costly cross prism and decreasing the required number of polarization beam splitters.
The present invention relates to a reflection liquid crystal projector designed for displaying a colored image, through a projector, on a screen by synthesizing a first, a second and a third color light (e.g., R, B and G lights) produced on a first, a second and a third reflection liquid crystal panel (e.g., LCD""s for R, B and G), the projector comprising a light source for outputting a white light, a polarized light conversion element for converting the white light outputted from the light source into either a P-polarized light or a S-polarized light for output, a color separation element for not only separating the polarized light outputted from the polarized light conversion element into the first, the second and the third colored lights but also for outputting the two color lights (e.g., B and G lights), differing in the direction of polarization but traveling in the same direction, out of the first, the second and the third color lights, while outputting the remaining one color light (e.g., R light) in a direction perpendicular to the direction of the two color lights (e.g., B and G lights), a first polarized beam splitter for not only permitting one (e.g., G light) of the two color lights to pass through but also reflecting the other (e.g., B light) to fall on corresponding reflection liquid crystal panels (e.g., LCD""s for G and B) for being outputted as reflected lights, a second polarization beam splitter for letting one colored light, the remainder of the color lights outputted from the color separation element falling on a corresponding one (e.g., LCD for R) of the first, the second and the third reflection liquid crystal panels so that the light can be outputted as a reflected light, and a dichroic prism for synthesizing the first, the second and the third color lights, outputted from the first and the second polarized beam splitters, for output to the projection lens.
In such a composition, the white light outputted from the light source by means of the polarized light conversion element is converted into either one (e.g., S-polarized light) of the S-polarized light or the P-polarized light; the polarized light is separated into the first, the second and the third color lights by the color separation element; the two color lights (e.g., B and G lights), differing in the direction of the polarization, out of the first, the second and the third color lights, are outputted in the same direction, while the remaining one color light,(e.g., R light) is outputted in a direction perpendicular to the output direction of the two color lights (e.g., B and G lights). The two color lights (e.g., G and B lights) outputted in the same direction from the color separation element are made to fall on corresponding reflection liquid crystal panels (e.g., LCD for G and B) by means of the first polarized beam splitter so that the reflected lights are outputted to the dichroic prism. The remaining one color light (e.g., R light), separated by the color separation element is made, by the second polarized beam splitter, to fall on a corresponding reflection liquid crystal panel (e.g., LCD for R) so that the reflected light is outputted to the dichroic prism. The dichroic prism synthesizes the first, the second and the third color lights outputted from the first and the second polarization beam splitters, and the synthesized light is projected, through the projection lens, to display the colored image on a screen.
Therefore, in the case of the present invention, not only the 3 sets of the polarized beam splitters necessary for the conventional projector can be reduced to 2 sets but also the costly cross prism as a color synthesizing element can be omitted, contributing to the realization of a low-price and lightweight projector.
In order to simplify the composition of the color separation element, the color separation element is made to comprise a first and a second dichroic mirror and a first and a second total reflection mirror. Of the polarized lights outputted from the polarized light conversion element, the first and the second color lights are allowed to pass through the first dichroic mirror while the third color light is reflected thereby. The first and the second color lights, which have passed through the first dichroic mirror, are reflected by the first total reflection mirror in a direction bent by 90xc2x0, while the third color light, reflected by the first dichroic mirror, is reflected by the second total reflection mirror in a direction bent by 90xc2x0; the second dichroic mirror not only permits one of the first and the second color lights, which have been reflected by the first total reflection mirror, to pass through it while reflecting the other but also reflects for output the third color light reflected by the second total reflection mirror. A phase element performs the functions described in (1) or (2) given below.
(1) The phase element is provided in the optical path by which the third color light reflected by the first dichroic mirror arrives at the second dichroic mirror through the second total reflection mirror so that the direction of the polarization of the third color light, which has been reflected by the first dichroic mirror, is converted by the phase element (e.g., conversion from the S-polarized light to P-polarized light).
(2) The phase element is provided in the light path by which the first and the second color lights, which have passed through the first dichroic mirror, arrive at the second dichroic mirror through the first total reflection mirror so that the direction of the polarization of the at least one of the first and the second colored lights is converted by the phase element (e.g., conversion from S-polarized light to P-polarized light).
For the simplicity of the construction, the color separation element is made to comprise the first, the second and the third dichroic mirrors, the total reflection mirror and the phase element so that the first dichroic mirror permits the transmission of the first and the second color light while reflecting the third color light out of the polarized lights which are outputted from the polarized light conversion element; the third dichroic mirror transmits one of the first and the second color lights, which have passed through the first dichroic mirror, while reflecting the other; the total reflection mirror reflects the third color light, which has been reflected by the first dichroic mirror, in a direction bent by 90xc2x0; the second dichroic mirror transmits the color light, which has been reflected by the third dichroic mirror, and reflects the color light, which has been reflected by the total reflection mirror, to make these color lights be outputted in the same direction; the phase element performs the function described in (1), (2) or (3) given below.
(1) The phase element is provided in the optical path through which the third color light, which has been reflected by the first dichroic mirror, arrives at the second dichroic mirror by way of the second dichroic mirror so that the direction of the polarization of the third color light, which has been reflected by the first dichroic mirror, is converted (e.g., from S-polarized light to P-polarized light) by the phase element.
(2) The phase element is provided in the optical path by which the first and the second color lights, which have passed through the first dichroic mirror, arrive at the third dichroic mirror so that the direction of the polarization of at least one of the first and the second color lights, which have passed through the first dichroic mirror, can be converted (e.g., from the S-polarized light to P-polarized light) by the phase element.
(3) The phase element is provided in the optical path by which the color light reflected by the third dichroic mirror arrives at the second dichroic mirror so that the direction of the polarization of the color light reflected by the third dichroic mirror can be converted (e.g. from S-polarized light to P-polarized light) by the phase element.
In order to eliminate the aberration occurring with the first and the second polarized beam splitters, the first and the second polarized beam splitter prisms are used instead of the first and the second polarized beam splitters. More particularly, the aberration occurring when the angle of incidence is not orthogonal can be eliminated by making the light fall on and be reflected orthogonally by each of the first and the second polarized beam splitters.
In order make the assembling easier by reducing the number of the parts, the first and the second polarized beam splitters and the dichroic prism are integrated into a prism block. That is, not only the number of the parts can be reduced but also the assembling of the parts can be made easier by integrating the first and the second polarization beam splitters and the dichroic prism into one prism block.
In order to simplify the composition of the phase element, a xc2xd wave plate, whose face is disposed orthogonally to the falling light, is employed as the phase element.
In order to dispense with a member for holding the phase element (a holder) for low cost and lightweight, as well as for reducing the optical path length, the phase element is composed of a total reflection mirror disposed so that its reflection face is at 45xc2x0 to the incoming color light and a xc2xc wavelength film securely attached to the reflection face of the total reflection mirror. More particularly, by forming the phase element with a xc2xc wavelength film attached securely to the reflection face of the total reflection mirror, the member for holding the phase element in position can be omitted, thereby contributing not only to the low cost and lightweight but also the reduction of the optical path length owing to the omission of the space which is necessary if the phase element is provided as an independent part.